The invention is based on a hydraulic valve control apparatus for an internal combustion engine as set forth herein after.
In a known hydraulic valve control apparatus of this type (German Offenlegungsschrift 3 511 820), the pressure line is controlled via a 3/2-way valve; in a special exemplary embodiment (FIGS. 8 and 9), the multi-position valve, in one switching position, connects the pressure line to the pressure chamber of a valve tappet, and in the other switching position connects it to the pressure chamber of a different valve tappet, using only a single liquid reservoir for both pressure chambers. Accordingly, for two engine inlet valves, one control position each of the magnet valve is used, and only one reservoir is used for both inlet valves. Especially at high rpm, the precision of control, or in other words how accurately the opening time cross section of the engine valve sought is attainable, depends on how large the total oil volume is that has to be shifted back and forth in control, and how many control conduits, with corresponding control cross sections, must be traversed. The magnet valve, especially, bears considerable responsibility for the expense and vulnerability to malfunction of this kind of hydraulic valve control apparatus; in engines having a typical maximum rpm, far from full utilization of the possible switching frequency of these magnet valves is made. A further factor is the burden due to the cost of every extra magnet valve.
In a hydraulic valve control apparatus of this type, it has also already been proposed (German Patent 38 15 668.7; U.S. Pat. No. 4,889,084) to embody the reservoir as a movable valve member; the end edge of the piston cooperates with a valve seat, so that the connection between the pressure line and reservoir chamber can be controlled. The reservoir piston simultaneously acts as an armature for a magnet valve that is open when without current, so that when the magnet is excited the pressure line is separated from the reservoir chamber. Although a combination of fluid reservoir and magnet valve, in which the same part serves as both the movable valve element of the magnet valve and as a reservoir piston, is attained by this provision, nevertheless one such "magnet valve reservoir unit" must be available for each valve control unit.